strptime handling space in fixed format string

Question

Is there a way to get strptime() to handle fixed format time strings?

I need to parse a time string that is always on the fixed width format: "yymmdd HHMMSS", but with the complication that leading zeros are sometimes present and sometimes not.

Reading up on the man(3p) page of strptime I note that for all the conversion specifiers %y, %m, %d, %H, %M, %S it is commented that "leading zeros shall be permitted but shall not be required.". Hence I try the format specifier %y%m%d %H%M%S, naïvely hoping that strptime will recognize that spaces in the two substrings %y%m%d and %H%M%S are equivalent to (missing) leading zeroes.

This seem to work for the specifier %m, but not for %M (well, unless the second part is less than 10) as demonstrated by the following piece of code

#include <stdio.h>
#include <time.h>


int main() {
   struct tm buff;
   const char ts[]="17 310 22 312";
   char st[14];

   strptime(ts,"%y%m%d %H%M%S", &buff);
   strftime(st,14,"%y%m%d %H%M%S",&buff);

   printf("%s\n",ts);
   printf("%s\n",st);
   return 0;
}

When compiled and run on my machine outputs

17 310 22 312
170310 223102

Any insight on how to overcome this would be appreciated, or do I need to resort to manually chopping the string 2-characters at the time using atoi to convert to integers to populate my struct tm instance with?

Answer 1

It would be best to get the code that generates the data with the wonky format fixed.

Assuming that can't be done this morning, then maybe you should canonicalize (a copy of) the wonky data, like this:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

static inline void canonicalize(char *str, int begin, int end)
{
    for (int i = begin; i <= end; i++)
    {
        if (str[i] == ' ')
            str[i] = '0';
    }
}

int main(void)
{
    struct tm buff;
    const char ts[] = "17 310 22 312";
    char st[32];

    char *raw = strdup(ts);

    printf("[%s] => ", raw);
    canonicalize(raw, 0, 5);
    canonicalize(raw, 7, 12);
    printf("[%s] => ", raw);
    strptime(raw, "%y%m%d %H%M%S", &buff);
    strftime(st, sizeof(st), "%y%m%d %H%M%S", &buff);
    printf("[%s] => ", st);
    strftime(st, sizeof(st), "%Y-%m-%d %H:%M:%S", &buff);
    printf("[%s]\n", st);
    free(raw);
    return 0;
}

The canonicalize() function converts replaces blanks with zeros over a given range of a string. Clearly, if you specify start and end points that are out of bounds, it will go trampling out of bounds. I preserved the const on ts and made a copy with strdup(); if you can treat the string as variable data, you don't need to make (or free) the copy.

The output from that code is:

[17 310 22 312] => [170310 220312] => [170310 220312] => [2017-03-10 22:03:12]